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IODP Expedition 383

Dynamics of Pacific Antarctic Circumpolar Current (DYNAPACC)


Daily Science Report for 18 July 2019

Location: In transit to Punta Arenas, Chile (midnight position 53°8.60′S, 67°20.30′W)

Science Update: Scientists presented the scientific results from Site U1544, met in small working groups to discuss postcruise research plans, and continued to write and revise the shipboard reports for Sites U1543 and U1544.

Today we transited 283 nmi at an average speed of 11.8 kt, crossing the Le Maire Strait at ~1000 h. We have 178 nmi remaining to Punta Arenas, Chile. The estimated time of arrival at Prat Terminal is around 1700 h on 19 July.


Daily Science Report for 17 July 2019

Location:
• Hole U1544A (55°32.2192′S, 71°35.6194′W; water depth 2089.9 mbsl)
• In transit to Punta Arenas, Chile (midnight position 56°5.20′S, 67°50.30′W)

Science Update: We started the day waiting for the seas to calm down to attempt to start a second hole at Site U1544. However, by 0600 h, the sea conditions had not improved sufficiently, and the decision was made to retrieve the drill string and to end operations at Site U1544. Before pulling up the pipe, the core line was run to 1900 m below rig floor (mbrf) and then lubricated as it was pulled back on the winch. The coring assembly was broken down and stowed away, the drill string was recovered, and the rig floor was secured for transit. At 1330 h, the JOIDES Resolution was underway to Punta Arenas, Chile.

In the laboratories, we finished processing the cores from Hole U1544A. We met to discuss individual postcruise research plans for the Chilean margin sites. We spent the second half of the day writing and reviewing the shipboard reports for Sites U1543 and U1544, and preparing presentations for tomorrow’s Site U1544 summary meeting.


Daily Science Report for 16 July 2019

Location: Hole U1544A (55°32.2192′S, 71°35.6194′W; water depth 2089.9 mbsl)

Science Update: We continued to APC core Hole U1544A with Cores 12H to 20F penetrating from 78.7 to 106.0 m below seafloor (mbsf), when heavy seas and 7+ m heave forced us to stop drill floor operations. The drill bit was raised out of the hole to 2055 m below rig floor (mbrf) and the ship was offset 20 m east of Hole U1544A to wait for the seas to calm down before attempting to start a second hole at this site. Cores U1544A-12H to 20F recovered 27.17 m with 99% recovery. The cores were not oriented and no formation temperature measurements were taken. All cores registered partial strokes and were advanced by recovery.

In the laboratories, scientists continued to process cores from Hole U1544A. Cores 10H through 20F were split, logged, and described. As in the upper nine cores, the sequence consists of alternating dark greenish gray silty clay and dark gray to very dark gray fine sands with sharp, erosive basal contacts and normal grading. Biosilica- and carbonate-bearing silty clays were restricted to several intervals in Cores 12H (79.5 to 82.3 mbsf) and 18F (94.5 to 98.3 mbsf), and are frequently interrupted by erosive normal graded sands.

Review and preparation of the reports for Sites U1543 and U1544 is ongoing.


Daily Science Report for 15 July 2019

Location: Hole U1544A (55°32.2192′S, 71°35.6194′W; water depth 2089.9 mbsl)

Science Update: Shortly after midnight, at 0015 h, we attempted to spud Hole U1544A with the bit positioned at 2092 mbrf, but we were unable to recover the core barrel. The core barrel was stuck, and presumed bent. We sheared the pins in the GS tool to detach it from the core barrel, pulled the sinker bars out of the drill string, and recovered the drill pipe and bit back aboard at 0615 h. Once the core barrel was back on the drill floor, we confirmed that it was bent and the bottom section was missing. The welder then cut off the bent section to remove the barrel from the pipe. At 0730 h, we decided to lower the drill string back to the seafloor and attempt to spud Hole U1544A with an XCB bit. We made up a new APC/XCB bottom-hole assembly without the nonmagnetic drill collar, and deployed the drill string down to the seafloor. With the ship offset 50 m at 225° southwest of the previous position, we deployed an XCB core barrel and drilled down slowly until we broke through the hard layer that previously had stopped the APC bit. Hole U1544A finally was spudded at 1330 h. When Core 1H was retrieved, we found a couple of ~5 cm size pebbles in the core catcher, but nothing else. For the remainder of the day we piston cored without incident to 78.7 mbsf. Cores 1H to 11H recovered 64.17 m with 85% recovery. The cores were not oriented and no formation temperature measurements were taken.

The upper 60 m of Hole U1544A (Cores 1H through 8H) were measured for physical properties and described. These consist of alternating dark greenish gray silty clay and dark gray to very dark gray fine sands with sharp, erosive basal contacts and normal grading. A prominent silt- and foraminifer-bearing nannofossil ooze was observed at the base of Core 4H (26–27 mbsf). Otherwise, the sediment is dominantly terrigenous.

We met to present and discuss some of the results from Site U1543, and we continued to work on the Site U1543 reports.


Daily Science Report for 14 July 2019

Location:
• In transit to Site U1544 (proposed Site CHI-1C)
• Hole U1544A (55°32.2002′S, 71°35.5836′W; water depth 2086.2 mbsl)

Science Update: The day started recovering the drill string back aboard at Site U1543. By 0110 h, the drill floor was secured for transit. The 184 nmi distance to Site U1544 (proposed Site CHI-1C) was covered in 15.4 h at a speed of 12 kt, and at 1746 h the ship was in dynamic positioning mode over the site coordinates. The rest of the day was spent assembling the APC/XCB bottom-hole assembly and deploying the drill string to the seafloor, reaching 2055 m below rig floor by midnight.

All remaining cores from Hole U1543B were measured for physical properties and described. The sediment in the deeper section of Hole U1543B consists primarily of dark greenish gray diatom- and silt-bearing clay. As in Hole U1543A, this section shows strong diagenetic coloring and lithification. Geochemical and paleomagnetic measurements of Site U1543 cores and samples are ongoing, and scientists continued to work on their reports for Site U1543.

The Co-Chief Scientists presented the scientific and operational objectives for Site U1544. The current plan for this site, based on the latest weather forecast, is to core two APC holes to ~50 mbsf, and then head to the eastern entrance of the Strait of Magellan, ahead of a strong weather system that is approaching the western margin of Chile and our operational area.


Daily Science Report for 13 July 2019

Location: Hole U1543B (55°35.0646′S, 76°40.5697′W; water depth 3865.3 mbsl)

Science Update: Today we completed coring operations in Hole U1543B and Site U1543. Cores U1543B-22H through 33H extended the hole from 180.5 m below seafloor (mbsf) to a final depth of 286.5 mbsf at 1630 h. We then began recovering the drill string aboard, clearing the seafloor at 1800 h. Total core recovery for Hole U1543B was 295.1 m (104%). The liners of Cores 25H, 31H, and 32H shattered during processing on the core receiving platform, and Cores 31H to 33H recorded partial strokes.

Cores U1543B-11H through 30H (77.2–258 mbsf) were measured for physical properties and described. As in Hole U1543A, this interval consists primarily of dark greenish gray diatom- and silt-bearing clay. Lithological variations mainly relate to changes in the relative diatom content, and only rare interbedding of light greenish gray diatom- and clay-bearing nannofossil ooze is observed. Strong diagenetic coloring, lithification, and deformation of Zoophycos burrows are characteristic in these deeper cores due to compaction. Drilling disturbance is generally low in this interval, except in Core 29H, where the upper three sections were strongly affected by brittle up-arching deformation.

Review of the Site U1542 reports is ongoing, and scientists began working on the Site U1543 reports. Scientists also presented their individual research plans for the Chilean margin sites.


Daily Science Report for 12 July 2019

Location: Hole U1543B (55°35.0646′S, 76°40.5697′W; water depth 3865.3 mbsl)

Science Update: We continued deepening Hole U1543B with Cores U1543B-5H through 21H penetrating from 21.7 to 180.5 mbsf and recovering 164 m (104%). The liners of Cores U1543B-20H and 21H shattered on the core receiving platform during processing.

Cores U1543B-1H through 10H (77.3 mbsf) were measured for physical properties, split, and described. Core U1543B-1H recovered the mudline, which consisted of a brown clay-bearing foraminifer-rich nannofossil ooze. As in Hole U1543A, Cores U1543B-1H through 10H consist primarily of dark greenish gray diatom- and silt-bearing clay. We observed one to two decimeter-scale gray carbonate-, clay-, and/or diatom-rich nannofossil ooze beds.

Review of Site U1542 reports is ongoing, and scientists began working on their reports from Site U1543.


Daily Science Report for 11 July 2019

Location:
• Hole U1543A (55°35.0631′S, 76°40.5900′W; water depth 3863.4 mbsl)
• Hole U1543B (55°35.0646′S, 76°40.5697′W; water depth 3865.3 mbsl)

Science Update: We completed APC coring in Hole U1543A after retrieving Cores U1543A-27H through 36H from a final depth of 339.6 m below seafloor (mbsf) at 1645 h. Core 36H experienced 90 klb of overpull upon retrieval. At that point, coring was ended without switching to the half-length APC system to provide enough time to drill another hole of equal penetration, and enable us to build a complete composite stratigraphic section at this site. Total core recovery in Hole U1543A was 350.62 m (103%). Hole U1543B was spudded 20 m east of Hole U1543A at 1915 h with the bit at 3868 m below the rig floor. The mudline core yielded just 1.14 m of sediment. The lower than expected recovery led us to drill down 1.9 m without recovery before taking the next core in order to stagger the core with Hole U1543A cores. Then, coring continued with Cores 2H through 4H from 3.0 to 21.7 mbsf by midnight, recovering 20.2 m (93%).

In the laboratories, measuring, analyses, and lithological description of Hole U1543A sediments continued through Core U1543A-33H (311.62 mbsf). Cores 24H through 33H consist primarily of greenish gray diatom and silt-bearing clay with rare decimeter-scale gray carbonate and diatom-rich nannofossil ooze beds in Sections 24H-4, 25H-6, 27H-1 through 4, 30H-1, and 31H-2. Authigenic carbonate was observed in the nannofossil ooze intervals in Cores 30H and 31H. High drilling disturbed intervals from suck-in were noted in the bottom two sections of Cores 30H through 33H. The sedimentary sequence unearthed from Hole U1543A spans from 6 Ma to the present. Review of Site U1542 reports is ongoing.


Daily Science Report for 10 July 2019

Location: Hole U1543A (55°35.0631′S, 76°40.5900′W; water depth 3863.4 mbsl)

Science Update: APC coring in Hole U1543A continued throughout the day, with Cores U1543A-12H through 26H penetrating from 102.1 to 244.6 mbsf and recovering 148.1 m (104%).

Cores U1543-6H to U1543-23H were measured for physical properties and described lithologically. Cores 6H to 13H consist of gray to greenish gray, slightly to moderately bioturbated silt-bearing clay. From Core 14H downhole, diatomaceous content becomes more common. Calcareous oozes are restricted to few decimeter-thick sparse layers, and an interval of light olive gray to gray diatom mats was observed in Core 23H. The scientific teams continued to work on their Site U1542 reports.


Daily Science Report for 9 July 2019

Location: Hole U1543A (55°35.0631′S, 76°40.5900′W; water depth 3863.4 mbsl)

Science Update: We started the day lowering the drill bit from 2866 to 3872 m below rig floor (mbrf) in preparation to spud Hole U1543A. The first core (1H) was taken at 0325 h, recovering 7.1 m. Core recovery determined a seafloor depth of 3863.4 mbsl. Soon after, at 0415 h, coring operations were suspended when one of the ship’s main propulsion shafts was shut down due to mechanical problems. The engineers found the problem to be with a faulty shaft brake unit. The brake was taken out of service and the shaft was brought back online by 0900 h. At that point coring resumed and continued without interruption throughout the day in good weather and sea conditions. Cores U1543A-2H through 11H extended the hole from 7.1 to 102.1 m below seafloor (mbsf) and recovered 96.16 m (101%).

Cores U1543A-1H through 7H were measured for physical properties, split, and described lithologically. Sediments are mainly gray to greenish gray, slightly to moderately bioturbated silt-bearing clay containing diatoms and radiolarians. They are interbedded with decimeter-scale beds of strongly bioturbated light greenish gray, clay-bearing nannofossil ooze containing traces of foraminifers. A comparison with results from a short pre-expedition site survey piston core suggests that the calcareous lithologies most likely reflect peak interglacial periods.

The scientific teams presented and discussed the results from Site U1542 and continued to work on their Site U1542 reports.


Daily Science Report for 8 July 2019

Location:
• Hole U1542D (52°42.300′S, 75°35.7742′W; water depth 1100.7 mbsl)
• In transit to Site U1543 (proposed Site ESP-1B)
• Hole U1543A (55°35.064′S, 76°40.590′W; water depth 3866 mbsl)

Science Update: We completed coring operations in Hole U1542D after recovering Core 27H from 213.7 mbsf (8.98 m recovered) at 0145 h. The drill string then was retrieved aboard, ending Site U1542. The drill floor was secured for transit, and by 0600 h we were underway to Site U1543 (proposed Site ESP-1B). The 119 nmi distance between the two sites was completed in 10.5 h at an average speed of 11.3 kt. Upon arrival at the Site U1543 coordinates at 1645 h, we lowered the thrusters and switched from cruising to dynamic positioning mode. The drill crew made up the APC/XCB bottom-hole assembly and began to lower the drill pipe down to the seafloor. By the end of the day, the drill bit had been lowered to 2866 m below the rig floor (mbrf).

The Co-Chief Scientists presented the primary objectives and the operations plan for Site U1543, where we aim to drill three holes to ~250 m. The scientific teams continue to analyze the Site U1542 core samples for paleomagnetic, geochemical, and physical properties; are working on their Site U1542 reports; and are preparing presentations for the site summary meeting.


Daily Science Report for 7 July 2019

Location:
• Hole U1542C (52°42.289′S, 75°35.775′W; water depth 1100.2 mbsl)
• Hole U1542D (52°42.300′S, 75°35.7742′W; water depth 1100.7 mbsl)

Science Update: Cores 29H (0.77 m recovered) and 30H (7.18 m recovered) deepened Hole U1542C to a final depth of 234 m below the seafloor (mbsf). Both cores registered partial strokes and were advanced by recovery. Then, we pulled the drill string out of the hole and moved the vessel 20 m south to start Hole U1542D. The bit was spaced out to 1107 m below the rig floor (mbrf), and Hole U1542D was spudded at 0600 h. The seafloor depth was determined by the recovery in the mudline core (4.8 m) at 1100.7 mbsl. Cores U1542D-2H to 26H penetrated from 4.8 to 204.7 mbsf, recovering 191.26 m of sediment (99%). Three intervals totaling 11 m were drilled without recovery to adjust offsets between cores from Holes U1542A to U1542D. Partial strokes were recorded on Cores U1542D-10H and 12H–26H.

Cores U1542C-29H and 30H and U1542D-1H through 27H were processed through the Core Laboratory. Paleomagnetic measurements are ongoing. Drilling disturbance in the lower part of Hole U1542D was generally much lower than in Hole U1542C, and this hole recovered an optimal sequence for the composite record at this site. The foraminifer-rich nannofossil ooze recovered in Hole U1542C at ~190–191 mbsf was observed at ~187–188 mbsf in Hole U1542D.

Sixty-five whole-round samples have been processed for interstitial water (IW) and the majority of the IW geochemical analyses have been completed. Forty-three sediment samples have been analyzed for CaCO3 content, and 39 samples have been analyzed for total carbon and total nitrogen content. Two significant peaks in CaCO3 content are observed at ~97 and ~125 mbsf in Hole U1542A.

The scientific teams started to work on their Site U1542 reports.


Daily Science Report for 6 July 2019

Location: Hole U1542C (52°42.289′S, 75°35.775′W; water depth 1100.2 mbsl)

Science Update: APC coring in Hole U1542C continued with Cores 11H to 21H penetrating from 88.8 to 172.3 mbsf by 0900 h, including two short intervals drilled without recovery to offset the core depths in Hole U1542C from those in Hole U1542A. Rigfloor activities then were paused once again due to heavy seas. This time, however, we waited for the seas to calm down with the drill bit at 71.8 mbsf inside the hole. At 1630 h, when the sea conditions had improved sufficiently, we washed down to bottom and continued APC coring. Cores 22H to 28H deepened Hole U1542C from 172.3 to 226 mbsf. Total core recovery for today was 133.5 m (97%).

Cores U1542B-1H and U1542C-21H to 28H were measured for physical properties, split, and described. Terrigenous clayey and silty dark greenish gray to dark gray sediments dominate the sequence. Layers with significant amounts of calcareous biogenic components are associated with interbedded sandy greenish gray silt. A foraminifer-rich nannofossil ooze was encountered at 190 to 191 mbsf. Drilling disturbance is much higher from Core 24H (~200 mbsf) downhole. Sampling for shipboard analyses was resumed in Core U1542C-19H.


Daily Science Report for 5 July 2019

Location:
• Hole U1542A (52°42.288′S, 75°35.792′W; water depth 1099.8 mbsl)
• Hole U1542B (52°42.288′S, 75°35.792′W; water depth 1101.1 mbsl)
• Hole U1542C (52°42.289′S, 75°35.775′W; water depth 1100.2 mbsl)

Science Update: Coring operations resumed at 1545 h, after sea conditions had improved. The drill bit was lowered from 1033 m below the rig floor (where it had been raised to the day before to wait on weather) to 1104 mbrf to start Hole U1542B. Hole U1542B was spudded at 1745 h, but the mudline core recovered just 1.46 m of soft sediment. Therefore, we decided to end the hole and start a new one. The bit was repositioned at 1105 mbrf, and Hole U1542C was spudded at 1830 h with Core U1542C-1H recovering 3.33 m. This determined the seafloor depth at 1100.2 m below sea level. APC coring continued to 79.3 mbsf with Cores 1H through 9H recovering 84.1 m (106%). A misfire was recorded on Core U1542C-8H.

Cores U1542A-14H to 20H were measured for physical properties, split into working and archive halves, and described. As in the first 13 cores, the lithology is predominantly greenish gray to dark gray terrigenous clayey silt and silt clay with minor biogenic components. Intervals with abundant foraminifers and calcareous nannofossils are limited to few decimeter-scale layers. Exceptionally high concentrations of foraminifers and nannofossils occurred in a light greenish gray layer at ~125 to 126 mbsf. Cores U1542A-15H, 16H, and 17H showed significant drilling disturbance. Biostratigraphic analyses suggest an age of ~0.4 Ma in Core 20H.

Cores U1542B-1H and U1542C-1H to 17H were measured for physical properties, split into working and archive halves, and described. Encountered lithologies closely resemble those of Hole U1542A, including the exceptionally light color nannofossil ooze identified again at ~125 mbsf in Hole U1542C.


Daily Science Report for 4 July 2019

Location: Hole U1542A (52°42.288′S, 75°35.792′W; water depth 1099.8 mbsl)

Science Update: We spudded Hole U1542A at 0215 h with the bit placed at 1108.4 m below rig floor. The mudline core retrieved 7.05 m of sediment, which determined a seafloor depth of 1099.8 m below sea level. Cores 1H to 19H deepened the hole to 165.6 mbsf, and recovered 178.2 m (108%). However, Core 19H registered a partial stroke and retrieved only 1.05 m. During the process of shooting this core, the shear pin in the GS tool sheared prematurely causing it to release from the core barrel. The sinker bars were brought back to the surface, and the GS tool was repaired before it was sent back to bottom to retrieve the core barrel. It took three subsequent wireline trips to recover the barrel finally at 2000 h. Once on the drill floor, we found that the cutting shoe was damaged, the core liner was shattered, and a large dropstone was found in the core catcher. We advanced the drill bit by 1.05 m, and then switched to the half-length APC (HLAPC) coring system on Core 20F to improve the chance of recovering a full core. Core 20F recovered 3.91 m. At 2245 h, the captain called the rig floor and stopped operations due to high seas.

Cores U1542A-1H to 13H were measured for physical properties, split into working and archive halves, and described. In contrast to the Central Pacific cores from Sites U1539–U1541, sediments at Site U1542, on the continental slope of southwestern Chile, are predominantly terrigenous. Dark gray clayey silt is interbedded with sandy, partly carbonate-bearing dark greenish silt on the decimeter scale. Dropstones >2 cm in size are rare to common throughout the cored interval, and well sorted thin mm- to cm-scale sandy layers occur sporadically. Drilling disturbance has been minimal, except in Core 10H, which showed strong soupy and suck-in deformation. Biostratigraphic analysis indicates that the base of Core 12H is within Marine Isotope Stage 7 (~0.21 Ma). All Site U1541 shipboard reports have been finalized.


Daily Science Report for 3 July 2019

Location:
• In transit to Site U1542 (proposed Site CHI-4B)
• Hole U1542A (52°42.288′S, 75°35.790′W; water depth 1100.5 mbsl)

Science Update: After 13 d of transit evading significant weather systems, we arrived at Site U1542 (proposed Site CHI-4B) at 1948 h. We lowered the thrusters and the vessel was placed over the site coordinates and on dynamic positioning mode by 2030 h. Soon after, the drill crew started to build and deploy the drill string to the sea bottom, lowering the drill bit to 708 m below rig floor by midnight.

The Co-Chief Scientists presented the scientific objectives and the operations plan for Site U1542 to the Science Party and IODP JRSO Technical Staff. The main objective at this site is to recover a continuous high-resolution sedimentary record that will allow us to (1) reconstruct intermediate water mass properties; (2) Patagonian ice-sheet variability; and (3) the dynamics of the Cape Horn Current, a northern branch of the Antarctic Circumpolar Current that provides a major portion of the present-day Drake Passage flow, since the Pliocene. The scientists are finalizing the Site U1541 shipboard reports and organizing working groups for postexpedition research.


Daily Science Report for 2 July 2019

Location: In transit to Site U1542 (proposed Site CHI-4B)

Science Update: Today the scientists presented a synthesis of the results from the Central South Pacific sites, and continued to work on the Site U1541 reports and discuss personal sample distribution and postexpedition research plans.

We continued to monitor weather systems moving across the South Pacific toward the operational area while transiting on a course of 109° southeast to proposed Site CHI-4B. We covered 260 nmi over the last 24 h at an average speed of 10.8 kt. With 228 nmi remaining, we estimate to arrive on site at 2030 h on 3 July.


Daily Science Report for 1 July 2019

Location: In transit to operational area in southwest Chilean margin

Science Update: The weather system we were monitoring moved past our projected course throughout the morning. Therefore, at 1316 h, we raised and secured the thrusters for transit, and we resumed navigation on a course of 122° southeast to our operational area in the southwest margin of Chile. We will determine which site to go to first based on weather conditions in the area. Today we transited 85 nmi and we have ~686 nmi remaining.

The science party continued to work on the Site U1541 reports and discuss personal sample distribution and postexpedition research plans. They also started to prepare presentations for a synthesis meeting about the results from the Central South Pacific sites.